A printer that executes bi-directional printing by combining forward printing with backward printing is known in the art. The print head in this type of printer has a plurality of nozzle groups for ejecting ink in a plurality of colors used for printing, such as cyan, magenta, yellow, and black. These groups of nozzles are arranged in a prescribed color order along the main scanning direction. As a consequence, when the printer performs bi-directional printing, the order of dots formed in different colors differs between forward printing and backward printing. Thus, in bi-directional printing, color tones produced in a partial image printed by forward printing (hereinafter called a “forward image”) may differ from a partial image printed by backward printing (hereinafter called a “backward image”).
A method described in US Patent Application Publication No. 2004/0174403 performs different gamma correction for forward images and backward images in order to suppress such differences in color tones produced between forward images and backward images.